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Pyyan / Compare / Claude Opus 4.8 vs Claude Fable 5.1

Claude Opus 4.8 vs Claude Fable 5.1

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Language Models · verified 2 Sept 2026

Claude Opus 4.8Anthropiccurrent
Claude Fable 5.1Anthropiccurrent
3 slots left
SpecificationClaude Opus 4.8Claude Fable 5.1
SummaryPrevious Opus flagship — warmer prose, strong long-horizon work.Same price as Fable 5, and cache reads cost a quarter of what they did.
Context1M1M
Input ($/Mtok)$5$10
Output ($/Mtok)$25$50
LicenceProprietaryProprietary
Max output128K128K
Parameters—Not published
Released—1 Sep 2026
Model IDclaude-opus-4-8claude-fable-5-1
CategoryLanguage ModelsLanguage Models
OfficialAnthropic ↗—

Highlighted rows are where these differ.

Claude Opus 4.8

  • Mid-session system messages supported
  • Adaptive thinking only — budget_tokens removed

Best for long-horizon agents.

Full spec sheet →

Claude Fable 5.1

  • Matches or beats Fable 5 at low and medium effort, and pulls clear at high effort
  • Cache reads cut to 25% of the old price, so re-reading a long context got much cheaper
  • Identical model to Mythos 5.1 underneath; the difference is the safeguards

Best for coding and long-running work.

Full spec sheet →